1. Field of the Invention
The invention is directed to an improved fuel injection device for an internal combustion engine of the type having a fuel pump for each cylinder of the engine.
2. Description of the Prior Art
A fuel injection device of this kind has been disclosed by EP 0 957 261 A1. For each cylinder of the engine, this fuel injection device has a fuel pump that has a pump piston that is driven into a stroke motion by the engine and delimits a pump working chamber to which fuel is supplied from a fuel tank. The pump working chamber is connected to a fuel injection valve that has an injection valve member, which controls at least one injection opening and can be moved in the opening direction, counter to a closing force, by the pressure prevailing in a pressure chamber connected to the pump working chamber. A first electrically controlled control valve is provided, which controls a connection of the pump working chamber to the fuel tank, which functions as a discharge chamber. A second electrically controlled control valve is also provided, which controls the control pressure prevailing in a control pressure chamber, which pressure acts at least indirectly on the injection valve member in the closing direction. In this known fuel injection device, it is disadvantageous that because the unpressurized fuel tank or the pressure side of a fuel-supply pump is used as a discharge chamber, the pressure in the pump working chamber and in the regions of the fuel injection device connected to it drops sharply when connected to the discharge chamber and thus presents the danger of cavitation. In addition, the efficiency of the fuel injection device is not optimal as a result of this.
The fuel injection device according to the invention has the advantage over the prior art that the pressure-holding valve maintains a pressure that is higher than the pressure in the discharge chamber so that the danger of cavitation is reduced and the efficiency is also improved. The pressure-holding valve also permits the simple execution of a preinjection at a limited pressure level.
In one embodiment, the pump working chamber is permitted to be decoupled from the pressure level maintained by the pressure-holding valve, which permits the prevention of leakage losses in the fuel pump.